Lecture 19- Pain Flashcards
What is nociception?
-activation of nociceptive primary afferents
What is pain?
-conscious, affective unpleasant somaesthic percept localized to the body
What is hyperalgesia?
-increased sensitivity to noxious stimuli
Does nociception have specialised neurons?
-yes
How can you map the receptive fields of nociception neurons?
-with heat
What is the pattern of response of nociception afferents?
- do not respond till sth really happens
- high threshold
- can be chemical burn too (whereas mechanorecpetors are very sensitive)
- only starts to fire at 45 degrees then at 60 degrees very repsonsive but the non-nociceptive thermoreceptor plateus
- nociceptors= encode for temps etc that damage, opposed to other recpetors
What are the two categories of pain?
- first (sharp pain)
- second (duller, burning pain)
What pain do the A delta fiber convey?
-small thinly myelinated fibres, 5 microns= fast sharp pain (mechanosensors at high threshold)
What pain do C fibres convey?
thinnest nerve fibres - unmyelinated= C fiber (here myelin would slow it down if it were here due to the small size) -1 micron= sensation of diffuse, duller burning pain -the C fibres are polymodal= respond to noxius chemical and mechanical stress when very high, respond to proton concentration (acidity)
What is the most common peripheral nerve fibre?
C fibres -small and everywhere
What are the characteristics of C fibres?
-0.2-1.5 micometers -0.5-2.0 meters for second speed -temperature, pain, itch
What are the characteristics of A delta fibres?
-myelinated -1-5 micrometers diameter -5-30 M/s -pain and temperature
What are the characteristics of A beta fibres?
-6-12 micrometers diameter -35-75m/s -mechanoreceptors of skin
What are the characteristics of A alpha fibres?
-13-20 micrometers in diameter -80-120m/s -proprioceptors od skeletal muscle
Where does capsaicin bind?
-can diffuse through the membrane so it binds on the inside -VR-1 receptor
What binds to VR-1 receptor?
-capsaicin -heat and H+ (acidity)
What is capsaicin in?
-jalapeno -red chilli -habanero
What is the nociception pathway like?
-cell body in dorsal root ganglia -small cell bodies -do their transmitting locally (segment or two) find their target cell in the superficial dorsal horn -crosses over right away -the second neuron goes to the thalamus
How is the nociception pathway different from the touch pathway?
-very different to the touch pathway wher eit was on the same side till brain stem -here it crosses over right away
What is the spinalthalamic tract?
-the nociception pathway -also called anterior lateral system (ALS)
Where in the spine do the C fibres terminate?
- in the superficial dorsal horn(the purple)
- in the marginal zone or substantia gelatinosa
Where in the spine do A delta fibres terminate?
can terminate in areas further away = even in the base of the dorsal horn as well as the superficial basal horn
Is there mixing of information from nociception afferents in the spinal cord?
-yes -one cell body can get information from A delta as well as C fibre
What would happen if your spinal cord was cut in half of its width?
- feel only one side of the body
- lose nociception on one side and touch on the other
- nociception intact on one side as it crosses over locally
- the touch pathway stays on one side whereas the pain crosses over right away
- brown sicard syndrom
What are the two main pathways of the anterolateral system?
1.Sensory-discriminative(the one to somatosensory cortex) 2.Affective-motivational (the one to insular and anterior cingulate cortex)
What is the anterolateral system pathway (detail)?
- from the spine goes to different parts of the brainstem/forebrain
- first division is to ventral posterior nucleus in the thalamus to the somatosensory S1 and S2
- second division goes to the amygdala, hypothalamus, periaquiductal grey, superior colliculus, reticular formation
- third division goes to the midline thalamic nuclei and from there to the insular cortex and anterior cingulate cortex
What are the functions of the anterolateral system pathway?
-the one to the insularn cortex and anterior cingulate cortex is the pahtway of how it feels, motivational and connected to learning -the one to the amygdala etc. is about the emotional feelings associated with pain -the one going to the somatosensory cortex, this is how we can tell where sth hurts, can loacte it
Where is the cingulate cortex?
anterior cingulate cortex (blue)= where the last neuron from the nociceptors ends (the third goes from brain stem to here)
-lot of emotional states include this cortex (hunger, thirst)
Where is the insular cortex?
- more cortex again after removing he upper bit of the cortex
- get lot of receptor input, from organs
What is the nociception pathway mediating discriminative aspects of temperature like for the body(picture)?
-
What is the nociception pathway mediating discriminative aspects of temperature like for the face (picture)?
trigeminal nucleus= pain and temp from the face and head
What is the trigeminal nucleus for?
trigeminal nucleus= pain and temp from the face and head
What appears in the tissue when tissue damage?
-bradykinin= when damage in cells -ATP= leaks when cell damage -more acidic environment -histamine -prostaglandin
What activates C fibres?
-presence of bradykinin, increase in ATP, 5-HT(serotonin),prostaglandin,histamine
What is the reflex within C fibres?
- reflex= within branches of this fibre
- nerve impulse to other branches and release substance P (peptide) and CGRP=dilation of blood vessels
- red because of inflammation
- positive feedback effect= activation leads to more activation in the other terminals
Is pain a homeostatic system?
-yes! maintaining integrity of the skin
What are phantom limbs?
-part of the body removed but they still feel like it’s there -ther is not a nerve saying this is your limb= this is constructed in the brain and that can exist without the mechanoreceptors
What are the descending systems that modulate the transmission of ascending pain signals?
- originates in the somatosensory cortex
- the raphe nuclei and all that line is in the brain stem! they project to the spinal cord to the first synapse in the anterolateral system
What happens at the first synapse of the anterolateral system when being modulated by ascending systems?
- this is how pain reduction occurs
- driven by cortical areas
- enkephalins are peptides
What is the dorsal column pathway fro visceral pain like?
- goes from the gut etc. to the spinal cord
- then synapses in the medulla and goes to the ventral posterior nuclear complex of the thalamus
- from there goes to the insular cortex
- in the medulla crosses over in the medial lemniscus
Is the idea of a pain pathway an oversimplification?
-yes
